The present invention relates broadly to a eddy current sensor apparatus, and in particular to a differential eddy current sensor apparatus for edge phasing of movable or deformable mirror segments.
The state of the art of edge sensing apparatus is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,397,357 issued to Metzker et al on Aug. 13, l968;
U.S. Pat. No. 3,961,243 issued to Schulz on June 1, 1976; and
U.S. Pat. No. 4,731,579 issued to Petersen et al on Mar. 15, 1988.
The Metzker et al patent discloses an inductive apparatus for centering a punch within its die. An annular housing which fits into the die cavity and has central passage to receive the punch. The housing contains two balanced inductors spaced equidistant from and on opposite sides of the desired path for the punch and connected to two legs of a balanced bridge circuit. When the punch is off-center, the impedances of the two inductors are unequal and the bridge circuit is unbalanced. The unbalanced bridge circuit is electrically detected and indicated.
The Schulz patent is directed to an inductive displacement transducer using a current measuring bridge circuit including a pair of adjustable electrical resistors coupled in series relationship in one half thereof, and a pair of series coupled induction coils and a movable magnetic armature in the other half of the bridge circuit. The improvement comprises a pair of series coupled electrical shunt resistors, each coupled to one of the induction coils.
The Petersen et al patent describes a magnetic position indicator using a pair of magnetic fields which are juxtaposed to each other such that they have opposite polarity and are of such a field strength that they provide for a generally linear variation in field strength extending over an elongated path which traverses the abutment of said fields.
In the prior art, edge sensors are utilized to measure or maintain incremental distances between structural elements. For example, edge sensors may be utilized to provide positional information about mirror segments which are part of large depoyable and deformable mirror. The edge sensors are utilized to maintain the shape of the desired optical surface and are needed to correct for phasing errors between the mirror segments. For complete control of such a mirror, the relative motion of each mirror segment with respect to its neighbor in three linear dimensions must be known.
The present differential eddy current sensor apparatus provides an edge sensing unit which can achieve sub-micro inch stability, avoidance of joint creep and insensitivity to temperature variation/gradients, gravity loading, and vibration disturbances.